The shaking table tests of a steel structure with innovative H type steel-unbuckling-braces (SUB) and with conventional central braces were conducted to compare the dynamic characteristics and seismic responses of the structure with one of the two kinds of braces. The effect of the two braces on seismic behaviors of the structure were analysed respectively. A finite element analysis was carried out and its result was compared with the experimental result. The results of tests and calculations show that the Innovative H type Steel-Unbuckling- Brace presented provides initial stiffness as the conventional central brace and the layer displacement of the two frameworks is almost the same in normal using. But the layer displacement of the framework with H type SUB is far less than that with conventional brace under middle and strong earthquakes, because the SUB dissipates earthquake input energy before the framework enters into the stage of elastic-plastic degeneration, which will reduce the structural damage.
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As a new type of prospective component for energy dissipation and vibration reduction, unbuckling-brace is a composite bracing member which can act as conventional central brace without buckling and displacement type damper, and overcomes the shortcoming of buckling characteristics of conventional braces. In this paper, H type steel-unbuckling-brace (SUB) which was welded by using steel flats and core made of low yield steel was presented at first. Quasi-static tests with reciprocating loads were conducted on four steel H type unbuckling-brace specimens for testing the seismic performances. The loading process and energy dissipation mechanism of these SUB specimens were studied, moreover, seismic performances, such as force-displacement hysteretic curve, resilience model, accumulative plastic deformation and energy dissipation capability are analyzed too. At last the hysteretic curves for the specimens were simulated based on ANSYS and compared with the experimental results. The better hysteretic behavior and high energy dissipation of SUB were verified. Numerical simulation results show that the frame structure with H type steel-unbuckling-brace has good seismic absorption effect.
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The strain paths and thermal cycles utilized during thermomechanical processing of two-phase alloys have a pronounced influence on the resulting distribution of grain orientations present and their spatial distribution. For example, large regions of similarly oriented α grains, commonly referred to as microtextured regions or macrozones,may persist despite the imposition of large macroscopic strains. The detrimental effect of microtexture on dwell fatigue life of high temperature alloys is well established; however,considerably less attention has been given to the effects of microtexture on fatigue life during continuous cycling . In the present work, the effects of microstructure and microtexture on the low cycle fatigue (N f≤ 104 cycles) behavior of Ti-6A1-4V have been characterized using electron microscopy. Microstructural parameters such as the volume fraction and size of the α phase were assessedby quantitative metallography while the contiguity of the α phase and the size and shape of the microtextured regions were investigated with electron backscatter diffraction. Variations in microstructure and microtexture due to subtle differences in thermomechanical processing routes have been correlated with variations in fatigue life through the use of quantitative fractography techniques. Using these methods the spatial and crystallographic orientations of fracture facets at small crack lengths have been determined. The results indicate that grains with c-axes are oriented between approximately 25° and 55° from the stress axis are most likely to form cracks that propagate by facet formation on the basal plane. Crack advance by faceted growth occurs readily through grains with similar basal plane orientation and,as a result,the contiguity of equiaxed α grains with basal poles in the 25°-55° range is an important parameter governing low cycle fatigue life.
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